(Not Applicable)
(Not Applicable)
This invention relates to array antennas and, more particularly, sector antennas which may be subject to interference signals incident at a fixed azimuth angle within the sector.
Array antennas may be employed to cover an azimuth sector. For example, for cellular communications, three antennas may provide omnidirectional coverage with each antenna having a radiation pattern, or beam, 120 degrees wide in azimuth.
Considering a single such antenna, sources of interference signals may be present and may be disruptive of reception of signals within its particular azimuth sector. To limit the effects of such interference, there have been proposed adaptive signal processing techniques capable of suppressing or reducing the effective antenna pattern gain at the azimuth angle of an interference source (i.e., reducing radiation pattern gain applicable to the azimuth angle at which interfering signals are incident at the antenna).
Adaptive signal processing and other prior techniques may typically have two particular attributes. First, such techniques may be capable of automatically steering a reduced gain pattern notch to the azimuth of an interference source and, further, may be capable of tracking the azimuth of such source as it moves. Second, such techniques are typically relatively complex and costly in implementation, and may be subject to operative frequency bandwidth limitations, as well as long-term reliability limitations. These factors may make the use of such techniques impractical in many applications. It should be noted that effects of interference can also be reduced or avoided by use of an antenna providing a narrow, focused radiation pattern (e.g., a fan beam). However, use of antennas with radiation patterns focused to provide coverage of only a narrow angular region may be impractical where the objective is to cover a relatively wide angular region (e.g., a 120 degree wide azimuth sector).
Accordingly, objects of the present invention are to provide new and improved array antennas which may have one or more of the following characteristics and capabilities:
low complexity, low cost provision of a radiation pattern notch;
radiation pattern notch fixed in azimuth;
radiation pattern notch at azimuth angle selected to correspond to incident angle of an interference source within a sector;
radiation pattern notch with gain null within notch;
undiminished gain outside of the notch; and
operation over a wide frequency band, with stable notch properties.
In accordance with the invention, an array antenna, to provide sector coverage with a radiation pattern notch at a selected angle ("THgr") within the sector, includes a horizontal linear array of radiating elements, with at least one left-side element and at least one right-side element, and a power divider/combiner. All left-side elements are arranged for nominally opposite-phase excitation relative to all right-side elements. The antenna also includes left and right coupling lines respectively coupled between the power divider/combiner and the left-side and right-side elements, with a left coupling line having a line-length differential (LL-LR) relative to a right coupling line. The line-length differential is selected to provide a phase differential between excitation of left-side and right-side elements to modify the nominally opposite-phase excitation to produce the radiation pattern notch at the selected angle ("THgr"), relative to array boresight.
The array antenna may include two or a higher even number of radiating elements. In presently preferred embodiments the power divider/combiner is configured to provide relative excitation amplitudes of: nominally 1 for each of the first pair of radiating elements, which are adjacent to array center; nominally 1/3 for each of a second pair of radiating elements, which if present are outwardly adjacent to the first pair; nominally 1/5 for each of a third pair of radiating elements, which if present are outwardly adjacent to the second pair; and nominally 1/7 for each of a fourth pair of radiating elements, which if present are outwardly adjacent to the third pair.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.